1. Field of the Invention
The present invention relates to an electronic circuit and more particularly a technology of an electronic circuit which compresses current data. Also the invention relates to an integrated circuit (IC) or a system circuit using the electronic circuit in one portion thereof, and more particularly a display device or an electronic apparatus having the IC or the system circuit.
2. Description of the Related Art
As electronic apparatus has been advanced in high performance, compactness (miniaturization) and low power consumption, an IC (integrated circuit) used inside thereof is required to be high in performance, small and highly integrated and such demands are further growing. A MOSFET (Field-Effect Transistor) IC using a conventional general bulk silicon (silicon wafer) has been progressed in performance, compactness and integration steadily up to now and this tendency is likely to continue.
An IC using a thin film transistor (TFT) is one of the ICs which are expected to be improved in performance, compactness and integration.
An active matrix type (AM type) liquid crystal display (LCD) using a polycrystalline silicon (polysilicon) TFF which has recently become used in a small display device field has a great advantage in that a driver circuit and the like can be integrated on a panel not only that a video signal can be stored in a pixel portion. That is, a module is large and complicated in a conventional PM type (passive matrix type) and an AM type which is using an amorphous silicon TFT because ICs separately fabricated into chips have to be used for a driver circuit and the like. In an AM type using a polysilicon TFT in which a driver circuit and the like are integrated on a panel, however, a module is greatly miniaturized.
Integration of a driver circuit and the like on a panel also plays a great role in realizing a fine-pitched display of display device. In the case where a driver circuit is not integrated on the panel, the finest possible pixel pitch in the display of display device is dependent on the interval between connecting terminals on the panel which connect an external IC to the panel. By integrating a driver circuit on the panel, this dependency no longer exists.
At present, only rather simple circuit represented by a driver circuit can be integrated on the panel in the AM type LCD using the polysilicon TFT. However, it is an inevitable subject to improve the circuit integrated on the panel in performance, compactness and integration in order to realize a more advanced, complicated and multifunctional panel.
There are various kinds of circuit to be newly integrated on the panel, including a circuit which compresses current data.
Just like in the AM type LCD, in an AM type OLED (Organic Light Emitting Diode) display device, a circuit integrated on the panel is required to be high in performance, compact and highly integrated. As for an OLED display device, only a PM type is put into practical use for the present, but an AM type using a polysilicon TFT is also now being developed rapidly aiming at practical use. Further, as the OLED is a current drive while the liquid crystal is a voltage drive, a means in which a video signal is processed as current data is becoming a mainstream in the OLED display device. In that case, a current data compression circuit is highly required when processing video signals.
The most common circuit which compresses current data is a current mirror circuit. FIG. 3 shows an example of the current mirror circuit.